The present invention relates to a communication system in which a plurality of devices communicate via a network. More specifically, the present invention relates to a surveillance system that retrieves information from sensors and a surveillance camera via a network.
In an example of a communication system for a surveillance system of the type which is actually in use today, an operation unit and a plurality of monitors in a surveillance center are used to retrieve information from a plurality of surveillance cameras and sensors via a network. In this type of surveillance system, communications take place over a network between individual surveillance cameras and. individual monitors, or between a plurality of sensors and an operation unit. This allows information to be sent from the surveillance cameras and sensors to the monitors and operation unit.
In this context, technologies to allocate bandwidth are known. These technologies assign bandwidth (capacity) beforehand for use by an individual communication, thus allowing separate communications to be performed without obstructing each other. For example, in the technology disclosed in Japanese laid-open patent publication number 10-42280, the total bandwidth is divided up according to the types of information to be sent in the surveillance system, and each division is assigned an available bandwidth. When the surveillance system is operating, the surveillance cameras and sensors send information to the monitors and the operation unit within the bandwidth assigned to the type of information being sent.
Japanese laid-open patent publication number 6-284148 presents another bandwidth restriction technology for communication systems. In this technology, a device performs peer to peer audio/video communications. When the communication throughput increases, only audio communications take place. When the communication throughput is reduced, both audio and video communications take place.
In technologies such as the one disclosed in Japanese laid-open patent publication number 42280, bandwidth is assigned in a fixed manner according to the type of information, to transferred. The rate at which information is generated over time may not be uniform, such during the transfer of information indicating an abnormality from a sensor or of control data such, as response commands issued from an operation unit operated by a user. If bandwidth assignments are based on the maximum transfer rate, there will be many time intervals during which the assigned bandwidths are not being used efficiently.
On the other hand, assigning bandwidth based on the average information transfer rate for information that is generated in a non-uniform manner over time will prevent responsive transfer of information when more information is being generated. This is not desirable, since it will result in a delay in the collection of important information that must be transferred rapidly, such as information relating to the presence of an abnormality or response commands.
Rather than pre-assigning bandwidth based on the type of information to be transferred, it would also be possible to transfer information according to the rate at which the information is generated. For example, if a large amount of information is generated all at once, individual communications will be affected in unpredictable ways by other communications, thus allowing communication problems to take place. These problems can result in the loss of various information, such as information relating to abnormalities, or control data, such as response commands.
If, in these cases, the audio/video communication technology disclosed in Japanese laid-open patent publication number 6-284148 is used, there would still be delays in the collection of important information that must be transferred rapidly, such as information relating to abnormalities and response commands.